qa: rsync test: exclude /usr/local

Some plana have non-world-readable crap in /usr/local/samba.  Avoid
/usr/local entirely for that and any similar landmines.

Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit 82211f2197241c4f3d3135fd5d7f0aa776eaeeb6)